Asphalt coatings have long been used to protect corrugated pipes against wear and corrosion for improved service life. Asphalt coatings have been applied by spraying, flowing or dipping asphalt over corrugated pipe surfaces, as noted by Cushman, U.S. Pat. No. 1,735,732, issued Nov. 12, 1929. The adherence of asphalt coatings may be improved by preheating pipe surfaces to approximately the temperature of the coating material prior to immersion in asphalt, as disclosed by Camerato, U.S. Pat. No. 2,114,975, issued Apr. 19, 1938.
The problem of adherence of asphalt coating materials to corrugated metal pipes remains, however, as abrasion and wear cause poorly bonded coatings to delaminate. As well, flood coated pipes are subject to delamination in chunks, and the heavy coating of asphalt in the troughs produced by flood coating further adds cost and weight to the coating. Accordingly, the need exits for improved asphalt coating materials, and improved methods for application of coating materials.